Dynamics of fast and slow magnetoacoustic waves in plasma slabs with thermal misbalance

Abstract

ABSTRACT The non-uniformity of the solar atmosphere along with the presence of non-adiabatic processes such as radiation cooling and unspecified heating can significantly affect the dynamics and properties of magnetoacoustic (MA) waves. To address the co-influence of these factors on the dispersion properties of MA waves, we considered a single magnetic slab composed of thermally active plasma. Using perturbation theory, we obtained a differential equation that determines the dynamics of the two-dimensional perturbations. Applying the assumption of strong magnetic structuring, we derived the dispersion relations for the sausage and kink MA modes. A numerical solution of the dispersion relations for coronal conditions was obtained to investigate the interplay between the non-uniformity and the thermal misbalance. For the heating scenario considered, it was found that the phase speed of both the sausage and the kink slow MA waves is strongly affected by the thermal misbalance in the long-wavelength limit. The obtained characteristic time-scales of the slow-wave dissipation coincide with the periods of waves observed in the corona. The phase speed of the fast waves, however, is not affected by the thermal misbalance. The geometry of the magnetic structure remains the main dispersion mechanism for the fast waves. Our analysis reveals that the dissipation of the fast waves is weaker than the dissipation of the slow waves under coronal conditions. The obtained results are of importance for the use of MA waves as a tool for estimating not only plasma parameters but also non-adiabatic processes.